Fire fighters from around the Peninsula battled the blaze. A blast believed to be caused by a natural gas explosion destroyed a San Bruno, Calif. neighborhood Thursday September 9, 2010.

Photo: Brant Ward, The Chronicle

Fire fighters from around the Peninsula battled the blaze. A blast...

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Three years after the blast, San Bruno Mayor Jim Ruane says more needs to be done by both PG&E and its regulators.

Photo: Michael Short, Special To The Chronicle

Three years after the blast, San Bruno Mayor Jim Ruane says more...

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San Bruno Mayor Jim Ruane talks about progress in rebuilding the Crestmoor neighborhood as the third anniversary nears of the PG&E gas line explosion nears, during a press conference held at San Bruno City Hall in San Bruno, CA Tuesday September 3, 2013.

Photo: Michael Short, Special To The Chronicle

San Bruno Mayor Jim Ruane talks about progress in rebuilding the...

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A fireman directed his hose at a house totally involved on the west side of the inferno. A blast believed to be caused by a natural gas explosion destroyed a San Bruno, Calif. neighborhood Thursday September 9, 2010.

Photo: Brant Ward, The Chronicle

A fireman directed his hose at a house totally involved on the west...

A Pacific Gas and Electric Co. engineer "mistakenly assumed" that parts of a major natural gas pipeline were safer than warranted during a lengthy records review aimed at reassuring the public in the aftermath of the 2010 San Bruno disaster, PG&E officials acknowledged.

PG&E made the admission in a filing to the state Public Utilities Commission, where administrative law judges have ordered a Friday hearing into the latest discrepancy in the utility's records to emerge from the Sept. 9, 2010, blast that killed eight people.

Regulators and federal investigators probing the explosion have cited widespread flaws in company records, which showed, among other things, that the pipe that ruptured in San Bruno was seamless. In fact, the pipe was riddled with flawed seam welds.

The utility - which faces more than $2 billion in potential fines for record-keeping and other violations related to the disaster - pledged afterward to conduct a massive effort to validate the records it keeps on its network of underground pipelines.

In 2011, after a records validation and pipeline testing effort on Line 147 in San Carlos - part of a larger system along the Peninsula that included the line that burst in San Bruno - PG&E persuaded state regulators to allow it to turn the pressure back up.

PG&E quietly disclosed in July, however, that it had found its effort had gaps and relied on faulty assumptions.

Human error

In the filing made with the Public Utilities Commission on Friday, PG&E gas transmission Vice President Kirk Johnson blamed "human error" for the problems that the utility had first disclosed in a meeting with regulators back in March.

He said the utility uncovered the flaws after an October 2012 corrosion-related leak, when repair crews found that the leaking section of Line 147 had a particular variety of at-risk seam weld down its length. This meant the pipeline was considered to be at a higher risk of rupture than the seam weld type reflected in PG&E records.

The leak, near the intersection of Rogers and Brittan avenues in San Carlos, was later repaired, and the utility launched a probe into the discrepancy.

"We determined our engineer had mistakenly assumed" the type of seam used on the pipe at that location, but had failed to indicate he had made such an assumption in verifying the safety of the line, Johnson said in the filing.

Validation gaps

PG&E concluded the line was verified "without the appropriate quality control steps," Johnson said.

By November, PG&E had found that three other nearby stretches of the line had inaccurate records. Some records suggested segments of the line had no potentially problematic seam welds, when in fact they did.

In the filing, Johnson acknowledged that PG&E's probe "revealed gaps in the early stages" of the validation effort on the line. He said such efforts have since been revamped.

PG&E also said it had relied on a legally inadmissible pressure test - in which water is fed into a line at high pressure - to document the safety of a part of nearby Line 101 in Millbrae.

For both lines, the utility said it had reduced gas pressure and plans to repair or replace the questioned segments. Johnson stressed that because the lines have been pressure-tested, the public is not at risk.

Mayor unhappy

But, as the three-year anniversary of the blast approaches, San Bruno Mayor Jim Ruane seized on the revelation, saying more needs to be done by both the utility and its regulators to assure safety.

"I thought: Here we go again - it's almost been three years, and the discovery of so much information and misinformation over this time is, it's actually disgusting," Ruane said.

"A lot of this stuff is coming to the surface now," he said. "I think PG&E - they have the opportunity to be the gold standard going forward - but every time, we see PG&E and (the Public Utilities Commission) stepping all over themselves."

State Sen. Jerry Hill, D-San Mateo, said the latest PG&E filing shows that very little has improved since the blast.

"The problem is, how many more pipelines are there out there where these same problems exist and can lead to the same devastating effect?" Hill said.

He said every filing is "just another excuse for poor management, and poor oversight."

Still rebuilding

The Sept. 9, 2010, rupture of a Pacific Gas and Electric Co. natural gas pipeline in San Bruno ignited a fire that killed eight people, destroyed 38 homes and set off a major rebuilding effort in the city's Crestmoor neighborhood - an effort that continues, slowly, three years later.

So far, 16 of the ruined homes are occupied after being rebuilt. Five more are under construction. The city is seeking a contractor to develop another 10 vacant lots owned either by San Bruno or by PG&E, which offered to buy lots from fire victims who chose not to rebuild. Construction is expected to begin next year.

City officials said two of the vacant lots will be retained, allowing for an expansion of a small neighborhood park and tot lot that was destroyed in the blast. Development of the park - along with final work on streets, sidewalks and streetlights - is expected to begin next year.

The cost of all infrastructure work is being paid from a trust fund, to which PG&E committed up to $50 million.